Primary requirements for any neurophysiological study of learning are stable phenomena in a preparation which can be subjected to experimental scrutiny. In the isolated brainstem preparation we have a unique opportunity: Both conditioning and habituation can be demonstrated, only a restricted associative region (the pontobulbar reticular formation) is functional, and much of the circuitry of the region is well known. Thus, the proposed research plan seeks to exploit some of the many opportunities provided by the isolated brainstem preparation. Because we have only recently begun to work with the conditioned eyeblink response, the conditioning studies in this proposal require a broader base than do the habituation studies. Therefore, a number of descriptive, but necessary, steps are required in order to define the ground for more focused, analytical studies of this phenomenon. The specific aims of this program include: 1. Determination of the minimal brainstem tissue necessary to support the conditioned eyeblink response. 2. Localization of reticular formation areas receiving inflow from the conditioning stimuli. 3. Analysis of response plasticity in sensory (acoustic and trigeminal relay nuclei), associative (reticular formation), and motor (facial motor nucleus) loci during eyeblink conditioning. Two temporal hierarchies of the isolated brainstem preparation will be utilized: a. Functional recovery in the isolated brainstem during evolving chronicity. b. The conditioned eyeblink response in the chronically isolated brainstem. 4. Analysis of response plasticity in acoustic relay nuclei during acoustic habituation. a) Cochlear nucleus studies; b) Inferior colliculus studies. Strategies for accomplishing these goals are enumerated in detail.